A longitudinal section through the human eye is shown schematically in FIG. 1. The axial length AL of the human eye is usually measured by a contact ultrasound method. Other measuring methods are described in DE 3201801, U.S. Pat. No. 5,673,096 and DE 4446183 A1. The curvature of the cornea-cornea radius HHR is determined by means of known keratometers/opthalmometers (DD 251497, U.S. Pat. Nos. 4,572,628, 4,660,946, 5,212,507 and 5,325,134). The measurement of the anterior chamber depth VKT can be carried out by ultrasound or by means of a unit added to a slit lamp (anterior chamber depth gauge, adjustment via the slit lamp image).
These measurements, which are also important for selecting the intraocular lens IOL to be implanted, must be determined particularly before a cataract operation, but also to monitor the progress of school children's myopia and to detect aniseikonia. In clinical practice, it is common to measure these quantities by means of at least two devices (e.g. ultrasonic a-scan and automatic keratometer). The measured quantities are used in formulas for calculating the optical power of the IOL. Various errors influencing the choice of IOL can occur depending on the type of device used.